The long-range objectives of this project are to 1) elucidate the detailed molecular events that take place during contraction and relaxation of cardiac and skeletal muscles, 2) to work out the molecular bases for the differences in contractile properties of the two muscles, and 3) to search for contractile protein abnormalities in diseased hearts. Immediate objectives are: 1) to try new methods for separation of myosin into "native" light and heavy chains, 2) if successful, to investigate the enzymatic and physical properties of myosins reconstituted from skeletal and cardiac light and heavy chains, 3) to re-examine myosins from left and right ventricles to determine if reported differences in their properties are indeed real, 4) to compare the physical and "relaxing" properties of cardiac and skeletal troponins, and 5) to compare the association properties of the contractile proteins--myosin, actin, tropomyosin and troponin--from cardiac and skeletal muscle. Only highly purified preparations of contractile proteins will be used in these studies, with careful analyses by gel electrophoresis. The analytical ultracentrifuge will be extensively used for the determination of accurate molecular weights and for the analysis of the association of protein systems. The use of the recently developed "television scanner" for absorption optics will permit more accurate measurements at very low protein concentration (several micrograms/ml).